JP2021083191A - Power control circuit - Google Patents

Abstract

To provide a power control circuit capable of lengthening a period for supplying power to a load to be backed up.SOLUTION: A power control circuit 1 includes: a lithium ion capacitor 40 charged by power supplied from an external power source 8; a first protection circuit 10 for supplying a discharge current of the lithium ion capacitor 40 to a first load 62; and a second protection circuit 20 for supplying the discharge current of the lithium ion capacitor 40 to a second load 62 that operates with power consumption smaller than that of a first load 61. When a terminal voltage of the lithium ion capacitor 40 becomes less than a first voltage, the first protection circuit 10 stops supplying a current to the first load 61. When the terminal voltage of the lithium ion capacitor 40 becomes less than a second voltage, the second protection circuit 20 stops supplying a current to the second load 62.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a power control circuit.

Conventionally, a secondary battery pack has been known in which a current that can perform the minimum function of an electric device is passed even after the voltage of the secondary battery used as a power source of the electric device drops and the discharge is stopped. For example, see Patent Document 1).

Japanese Unexamined Patent Publication No. 2006-158028

It is required to extend the period for supplying power to the load to be backed up.

The present disclosure has been made in view of the above points, and an object of the present disclosure is to provide a power control circuit capable of prolonging the period for supplying power to a load to be backed up.

In the power control circuit according to some embodiments, the power is supplied from the external power source to the lithium ion capacitor charged by the power supplied by the external power source and the first load operated by the power supplied by the external power source. A first protection circuit that supplies the discharge current of the lithium ion capacitor when it is no longer supplied, and a second load that operates with the power supplied by the external power supply and operates with less power consumption than the first load. On the other hand, the first protection circuit includes a second protection circuit that supplies the discharge current of the lithium ion capacitor when power is no longer supplied from the external power source, and the first protection circuit has a terminal voltage of the lithium ion capacitor. When the voltage becomes less than one voltage, the supply of current to the first load is stopped, and the second protection circuit is used when the terminal voltage of the lithium ion capacitor becomes less than the second voltage lower than the first voltage. The supply of current to the second load is stopped. By doing so, when the lithium ion capacitor is used as a backup power source for the first load and the second load, the power control circuit stops the first load while leaving the charge amount of the lithium ion capacitor at least a predetermined value. Be done. As a result, the period during which power can be supplied to the second load becomes longer.

In the power control circuit according to the embodiment, the first protection circuit controls the first switching element connected between the lithium ion capacitor and the first load, and the first switching element. A voltage detection circuit is provided, and the first voltage detection circuit is configured to be operable by a current supplied from the lithium ion capacitor via the first switching element when power is no longer supplied from the external power supply. When the terminal voltage of the lithium ion capacitor is equal to or higher than the first voltage, the first switching element is maintained in the ON state, and when the terminal voltage of the lithium ion capacitor becomes less than the first voltage, the first switching element is maintained. 1 The switching element may be transitioned to the off state. By doing so, the first protection circuit does not consume unnecessary power after the first load is stopped. As a result, the period during which power can be supplied to the second load becomes longer.

In the power control circuit according to one embodiment, the first protection circuit is configured so that the lithium ion capacitor can be connected to an external power supply via the first switching element, and the first switching element transitions to an off state. Even in this case, the current may be configured to flow from the external power source to the lithium ion capacitor. By doing so, the lithium ion capacitor is charged when the external power source is restored, regardless of the state of the first protection circuit. As a result, recovery at the time of power recovery becomes easy.

In the power control circuit according to one embodiment, the lithium ion capacitor is mounted on a circuit board together with the first load, and the temperature of the lithium ion capacitor increases as the calorific value of the first load increases. The lower limit of the terminal voltage of the ion capacitor corresponds to the first voltage when the temperature of the lithium ion capacitor is higher than the predetermined temperature, and when the temperature of the lithium ion capacitor is equal to or lower than the predetermined temperature. It may correspond to the second voltage. By doing so, the lithium ion capacitor is utilized in the widest possible voltage range within the operating temperature range. As a result, the period during which power can be supplied to the second load becomes longer.

According to the present disclosure, there is provided a power control circuit capable of extending the period for supplying power to the load to be backed up.

It is a circuit diagram of the power control circuit which concerns on Comparative Example 1. It is a circuit diagram of the power control circuit which concerns on Comparative Example 2. It is a circuit diagram which shows the structural example of the power control circuit which concerns on one Embodiment. It is a circuit diagram which shows the structural example of the 1st protection circuit. It is a circuit diagram which shows the structural example of the 2nd protection circuit. It is a graph which shows an example of the time change of the terminal voltage of a lithium ion capacitor. It is a figure which shows the configuration example in which a lithium ion capacitor and a 1st load are mounted on a substrate.

An embodiment according to the present disclosure will be described in comparison with a comparative example.

(Comparative Example 1)
As shown in FIG. 1, the power control circuit 910 according to Comparative Example 1 includes a power supply 911, a processor 912, and an RTC (Real Time Clock) 913. The power supply 911 supplies power to the processor 912. If the power supply 911 is unable to supply power, the processor 912 stops operating.

The power control circuit 910 further includes a diode 914 connected in series with the RTC 913 and an electric double layer capacitor 915 connected in parallel with the RTC 913. The power supply 911 supplies electric power to the RTC 913 and supplies electric power to the electric double layer capacitor 915 to charge the electric double layer capacitor 915 via the diode 914. When the power supply 911 cannot supply power, the electric double layer capacitor 915 discharges and supplies power to the RTC 913. The RTC 913 can be operated by the electric power discharged from the electric double layer capacitor 915. As a result, the power control circuit 910 can function as a backup power source for the RTC 913.

However, the electric double layer capacitor 915 tends to self-discharge. Therefore, the electric double layer capacitor 915 is not suitable for the purpose of backing up the load for a long period of time.

In FIG. 1, when the electric double layer capacitor 915 is replaced with a primary battery such as a button battery, the primary battery can function as a backup power source for the RTC 913. However, the primary battery cannot be charged and needs to be replaced. It is also necessary to add a circuit so that the primary battery starts backup when the power supply 911 is stopped.

Further, the power control circuit 910 can back up only one system connected to the RTC 913, and it is necessary to separately provide a backup power supply for the processor 912.

(Comparative Example 2)
As shown in FIG. 2, the power control circuit 920 according to Comparative Example 2 includes a lithium ion secondary battery 921, a positive electrode terminal 926, and a negative electrode terminal 927. The lithium ion secondary battery 921 may include a plurality of battery cells. The positive electrode of the lithium ion secondary battery 921 is connected to the positive electrode terminal 926. The negative electrode of the lithium ion secondary battery 921 is connected to the negative electrode terminal 927. The positive electrode terminal 926 and the negative electrode terminal 927 are connected to the load. The power control circuit 920 functions as a backup power source for the load by supplying a current to the load from the positive electrode terminal 926 and the negative electrode terminal 927. The charge rate (SOC: State of Charge) of the lithium ion secondary battery 921 has a positive correlation with the terminal voltage. That is, the higher the terminal voltage of the lithium ion secondary battery 921, the higher the SOC. The lithium ion secondary battery 921 can be discharged for a long time as the SOC is higher.

The load includes a heavy load operating with power consumption equal to or higher than a predetermined value and a minute load operating with power consumption less than a predetermined value. Heavy loads include, for example, processor 912. Microloads include, for example, RTC913.

The negative electrode of the lithium ion secondary battery 921 and the negative electrode terminal 927 of the power control circuit 920 are connected by two parallel paths. One path includes switch 923. Another path includes a series circuit of switch 924 and resistor 925. The switches 923 and 924 are made conductive so that a current can flow through the wiring in the closed state. The switches 923 and 924 are cut off so that no current flows through the wiring in the open state.

The power control circuit 920 further includes a switch control unit 922 that controls the opening and closing of the switches 923 and 924. The switch control unit 922 controls the switches 923 and 924 based on the voltage of the lithium ion secondary battery 921.

The switch control unit 922 closes the switch 923 and opens the switch 924 when the voltage of the lithium ion secondary battery 921 is equal to or higher than a predetermined voltage, that is, when the SOC is equal to or higher than a predetermined value. In this case, the terminal voltage of the lithium ion secondary battery 921 is output as a voltage between the positive electrode terminal 926 and the negative electrode terminal 927, and is applied to the load connected between the positive electrode terminal 926 and the negative electrode terminal 927.

The switch control unit 922 opens the switch 923 and closes the switch 924 when the voltage of the lithium ion secondary battery 921 is less than the first predetermined value, that is, when the SOC is less than the predetermined value. In this case, the lithium ion secondary battery 921 supplies current to the load via the wiring including the resistor 925. The switch control unit 922 measures the discharge current of the lithium ion secondary battery 921 based on the voltage of the resistor 925. When the discharge current of the lithium ion secondary battery 921 exceeds a predetermined value, the switch control unit 922 opens the switch 924 and stops the discharge of the lithium ion secondary battery 921. The switch control unit 922 closes the switch 924 after confirming that the discharge current of the lithium ion secondary battery 921 is less than a predetermined value, and restarts the discharge of the lithium ion secondary battery 921. By doing so, the discharge current of the lithium ion secondary battery 921 is limited, and the duration of discharge is lengthened.

When the current supply is stopped, the load cuts off the wiring that supplies the current to the heavy load while conducting the wiring that supplies the current to the minute load by means such as opening and closing the switches 923 and 924. By doing so, the current supplied to the entire load is controlled to be less than a predetermined value. As a result, the switch control unit 922 can confirm that the current flowing through the load becomes less than a predetermined value when the switch 924 is closed. In this case, the power control circuit 920 can function as a backup power source for a minute load.

As described above, the power control circuit 920 can function as a backup power source not only for a minute load but also for a heavy load. The power control circuit 920 supplies backup current to both a minute load and a heavy load from one system composed of a positive electrode terminal 926 and a negative electrode terminal 927. In other words, the power control circuit 920 draws backup current from one system by both micro and heavy loads. Only when the heavy load itself stops its operation does the current suction by the heavy load stop. Therefore, the operation of the power control circuit 920 to supply the current only to the minute load depends on the control of the heavy load itself.

In the resistor 925 used for measuring the discharge current of the lithium ion secondary battery 921, power consumption that does not contribute to the operation of the load is generated. Such power consumption reduces the time that the lithium ion secondary battery 921 can continue to discharge.

The lithium ion secondary battery 921 has a narrow usable temperature range and can be used only under limited conditions. When the power control circuit 920 is used in an environment that does not meet the conditions, its reliability is reduced.

The lithium ion secondary battery 921 is easy to self-discharge. Therefore, the lithium ion secondary battery 921 is difficult to be stored as an inventory for a long period of time, and is not suitable for a long-term load backup application.

The lithium ion secondary battery 921 deteriorates or breaks down quickly due to overcharging. Therefore, it is necessary to control the charging current of the lithium ion secondary battery 921 by the overcharge protection circuit. The power control circuit 920 is less likely to be miniaturized by providing the overcharge protection circuit. As a result, the installation location of the power control circuit 920 is limited.

The problem of the lithium ion secondary battery 921 described above is a problem that can occur similarly even when the electric double layer capacitor 915 is replaced with the lithium ion secondary battery 921 in FIG. 1.

As described above, in the configuration according to each comparative example, the power control circuits 910 and 920 have various problems for backing up the load for a long period of time.

Therefore, the present disclosure describes a power control circuit 1 (see FIG. 3 and the like) capable of backing up a load for a long period of time. The power control circuit 1 may be applied to an edge computer gateway application. The power control circuit 1 may be used in an IoT (Internet of Things) gateway terminal.

(One Embodiment of the present disclosure)
As shown in FIG. 3, the power control circuit 1 according to the embodiment includes a lithium ion capacitor 40, a first protection circuit 10, a second protection circuit 20, and a regulator 30. The lithium ion capacitor 40 is connected to the grounding point 80 at one end and is connected to the first protection circuit 10 and the second protection circuit 20 at the other end. The first protection circuit 10 is connected to the lithium ion capacitor 40 at one end and to the regulator 30 at the other end. The regulator 30 is connected to the first protection circuit 10 at one end and to the first load 61 at the other end. The second protection circuit 20 is connected to the lithium ion capacitor 40 at one end and is connected to the second load 62 via the diode 52 at the other end. The diode 52 is connected with the direction from the second protection circuit 20 toward the second load 62 as the forward direction. The power control circuit 1 has a node 71 located between the regulator 30 and the first load 61, and a node 72 located between the diode 52 and the second load 62. The power control circuit 1 further includes a diode 51. The diode 51 is connected between the node 71 and the node 72 with the direction from the node 71 to the node 72 as the forward direction. The power control circuit 1 is connected to the external power supply 8 between the first protection circuit 10 and the regulator 30.

The regulator 30 controls the electric power supplied from the external power source 8 so that the voltage or current becomes a predetermined value, and supplies the electric power to the first load 61 and the second load 62. The regulator 30 may be configured as a switching regulator. The regulator 30 may be configured as a step-down switching regulator or a step-up switching regulator.

The lithium ion capacitor 40 is a power storage device capable of realizing performance that combines the advantages of the electric double layer capacitor 915 and the lithium ion secondary battery 921. The lithium ion capacitor 40 can be discharged for a long time as it is charged with a large amount of electric charges. The amount of charge charged in the lithium ion capacitor 40 has a positive correlation with the terminal voltage. That is, the higher the terminal voltage of the lithium ion capacitor 40, the larger the amount of electric charge charged. As a result, the higher the terminal voltage, the longer the lithium ion capacitor 40 can be discharged.

The external power supply 8 can supply electric power to the regulator 30 and charge the lithium ion capacitor 40 via the first protection circuit 10. The external power supply 8 may include a circuit that controls the charging voltage of the lithium ion capacitor 40. The external power supply 8 may have, for example, a charge upper limit voltage protection function of the lithium ion capacitor 40. The external power supply 8 may control the voltage for charging the lithium ion capacitor 40 and the voltage applied to the regulator 30 to the same voltage or different voltages.

The electric power supplied by the external power source 8 is supplied to the first load 61, the second load 62, and the lithium ion capacitor 40. The regulator 30 controls the electric power supplied from the external power source 8 to DC electric power having a predetermined voltage and supplies the electric power to the first load 61 and the second load 62. The lithium ion capacitor 40 is charged with the electric power supplied from the external power source 8. The external power supply 8 may include a charge control circuit that controls charging of the lithium ion capacitor 40. The external power supply 8 may control the output voltage so that the lithium ion capacitor 40 can be charged in the CCCV (Constant Current, Constant Voltage) mode. The regulator 30 can supply DC power of a predetermined voltage to the first load 61 and the second load 62 regardless of the magnitude of the voltage controlled by the external power source 8 to charge the lithium ion capacitor 40.

When the external power supply 8 is stopped and power cannot be supplied, the lithium ion capacitor 40 is discharged to supply power to the first load 61 or the second load 62. The first protection circuit 10 and the second protection circuit 20 control whether to flow or cut off the current based on the terminal voltage of the lithium ion capacitor 40.

When the terminal voltage of the lithium ion capacitor 40 is equal to or higher than the first voltage, the first protection circuit 10 conducts the lithium ion capacitor 40 and the regulator 30 to supply electric power from the lithium ion capacitor 40 to the regulator 30. .. When the voltage of the lithium ion capacitor 40 is less than the first voltage, the first protection circuit 10 cuts off between the lithium ion capacitor 40 and the regulator 30 and stops the power supply to the regulator 30.

When the voltage of the lithium ion capacitor 40 is equal to or higher than the second voltage lower than the first voltage, the second protection circuit 20 conducts the lithium ion capacitor 40 and the second load 62 to conduct power from the lithium ion capacitor 40. Is supplied to the second load 62. When the voltage of the lithium ion capacitor 40 is less than the second voltage, the second protection circuit 20 cuts off between the lithium ion capacitor 40 and the second load 62, and stops the power supply to the second load 62.

From the above, when the voltage of the lithium ion capacitor 40 is equal to or higher than the first voltage, the first load 61 and the second load 62 can be operated by supplying electric power from the lithium ion capacitor 40. When the voltage of the lithium ion capacitor 40 is less than the first voltage and equal to or more than the second voltage, the second load 62 can be operated by supplying power from the lithium ion capacitor 40. On the other hand, the first load 61 cannot operate without being supplied with electric power. When the voltage of the lithium ion capacitor 40 is less than the second voltage, both the first load 61 and the second load 62 cannot operate without being supplied with electric power.

The power control circuit 1 cuts off the power supply to the first load 61 when the voltage of the lithium ion capacitor 40 becomes less than the first voltage, so that the charge amount of the lithium ion capacitor 40 remains at least a predetermined value. The first load 61 can be stopped with. By doing so, the amount of electric power that can be supplied to the second load 62 is secured. As a result, the period during which electric power can be supplied to the second load 62 becomes longer.

As described above, the power control circuit 1 according to the present embodiment can function as a backup power source for supplying power to the first load 61 and the second load 62 when the external power source 8 cannot supply power. .. Further, the power control circuit 1 can preferentially supply power to the second load 62 which needs to be operated for at least a predetermined period when the charge amount of the lithium ion capacitor 40 decreases. As a result, the power control circuit 1 can back up the second load 62 for a predetermined period while functioning as a backup power source for the first load 61 and the second load 62.

The second load 62 includes a clock circuit such as an RTC. The power control circuit 1 supplies backup power to the IoT terminal when applied to an edge computer gateway application. The IoT terminal uploads data to the server by communicating with the server or the like. Communication between the IoT terminal and the server or the like is synchronized by a clock. Therefore, in the operation of the IoT terminal, the clock operation is included in one of the operations that should be maintained preferentially. The power control circuit 1 according to the present embodiment can satisfy the specifications as a backup power source in the application of the edge computer gateway.

The first load 61 includes a processor and the like. The first load 61 may be configured to consume the amount of electric power that can be supplied by the lithium ion capacitor 40 in about several tens of seconds. On the other hand, the second load 62 may be configured to consume the amount of electric power that can be supplied by the lithium ion capacitor 40 over about half a year or about one year or more. That is, the power consumption of the second load 62 may be orders of magnitude smaller than the power consumption of the first load 61. By doing so, even if the IoT terminal in which the power control circuit 1 is adopted is installed in a position where it is difficult for the worker or the like to access it, until the worker repairs it after the power is not supplied from the external power supply 8. It can continue to function as a backup power source for the second load 62.

The second load 62 may include a storage device such as a SRAM (Static Random Access Memory). When the power supply from the external power source 8 is stopped, the storage device as the second load 62 may quickly store the information being processed by the processor or the like. By doing so, when the power supply from the external power source 8 is restarted, the processor can restart the operation based on the information before the stop.

The second voltage corresponds to the lower limit voltage defined as the specifications of the lithium ion capacitor 40. When the lithium ion capacitor 40 is discharged until the terminal voltage of the lithium ion capacitor 40 becomes less than the lower limit voltage, there is a high possibility that the lithium ion capacitor 40 will fail.

The first voltage is set based on the power consumption of the second load 62 and the time for backing up the second load 62. That is, the amount of electric charge discharged until the terminal voltage of the lithium ion capacitor 40 drops from the first voltage to the second voltage is equal to or greater than the amount of electric charge required to back up the second load 62 over a predetermined period. , The first voltage is set.

As shown in FIG. 4, the first protection circuit 10 includes a voltage detection circuit 11, a switching element 16, and terminals 17 and 18. The voltage detection circuit 11 is also referred to as a first voltage detection circuit. The switching element 16 is also referred to as a first switching element. The first protection circuit 10 is configured to be connectable to the lithium ion capacitor 40 at the terminal 17. The first protection circuit 10 is configured to be connectable to the regulator 30 and the external power supply 8 at the terminal 18. The first protection circuit 10 is connected to the grounding point 80 by the voltage detection circuit 11. The first protection circuit 10 operates by the voltage applied between the terminal 17 or 18 and the grounding point 80.

In the present embodiment, the switching element 16 includes a p-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching element 16 may include an n-channel MOSFET. The switching element 16 may include a transistor other than the MOSFET, or may include a switch IC (Integrated Circuit) or the like. The switching element 16 conducts in the on state and shuts off in the off state.

The voltage detection circuit 11 includes a comparator 12, a reference voltage source 13, and voltage dividing resistors 14 and 15. The voltage dividing resistors 14 and 15 are connected in series between the terminal 18 and the grounding point 80. The voltage dividing resistors 14 and 15 divide the voltage applied between the terminal 18 and the grounding point 80. The voltage obtained by dividing the voltage applied between the terminal 18 and the ground point 80 by the voltage dividing resistors 14 and 15 is also referred to as a first voltage dividing voltage. The first voltage dividing voltage is applied to the node 19 located between the voltage dividing resistor 14 and the voltage dividing resistor 15. The reference voltage source 13 is connected between the terminal 18 and the grounding point 80, and outputs the first reference voltage.

The comparator 12 is connected to the reference voltage source 13 and the node 19 at the input terminal, and is connected to the gate of the switching element 16 at the output terminal. The comparator 12 is connected between the terminal 18 and the grounding point 80, and operates by the voltage applied between the terminal 18 and the grounding point 80. When the switching element 16 is turned on to conduct the terminal 17 and the terminal 18, the comparator 12 may operate at the voltage applied from the terminal 17 or may operate at the voltage applied from the terminal 18. You may. The comparator 12 has two input terminals and one output terminal. The comparator 12 outputs a signal from the output terminal based on the result of comparing the first reference voltage and the first voltage dividing voltage input to the input terminal.

When the first voltage dividing voltage is equal to or higher than the first reference voltage, the comparator 12 outputs a signal for controlling the switching element 16 to be in the ON state from the output terminal. When the switching element 16 is an FET, the comparator 12 outputs a signal having a voltage equal to or higher than the gate threshold voltage of the FET. When the first voltage dividing voltage is equal to or higher than the first reference voltage, the comparator 12 may turn on the switching element 16 by outputting the same voltage as the terminal 17 or 18. The switching element 16 maintains the ON state by receiving a signal that controls the switching element 16 to be in the ON state when it is in the ON state. The switching element 16 transitions to the on state by receiving a signal that controls the switching element 16 to be turned on when it is in the off state.

When the first voltage dividing voltage is less than the first reference voltage, the comparator 12 outputs a signal for controlling the switching element 16 to be in the off state from the output terminal. When the switching element 16 is an FET, the comparator 12 outputs a signal having a voltage lower than the gate threshold voltage of the FET. When the first voltage dividing voltage is less than the first reference voltage, the comparator 12 may turn off the switching element 16 by outputting the same voltage as the grounding point 80. The switching element 16 transitions to the off state by receiving a signal that controls the switching element 16 to be in the off state when it is in the on state. When the switching element 16 transitions to the off state, the comparator 12 cannot receive the voltage and does not operate. The comparator 12 does not output a signal when it cannot receive the voltage and does not operate. The state in which the comparator 12 does not output a signal is considered to be a state in which the comparator 12 outputs a signal that turns off the switching element 16. Therefore, when the comparator 12 does not output a signal, the switching element 16 is turned off. As a result, the switching element 16 is maintained in the off state after transitioning from the on state to the off state. Even when the switching element 16 is originally in the off state, the switching element 16 is maintained in the off state.

The voltage detection circuit 11 is configured so that the first voltage dividing voltage becomes equal to or higher than the first reference voltage when the terminal voltage of the lithium ion capacitor 40 is equal to or higher than the first voltage. Specifically, in the voltage detection circuit 11, the resistance values of the voltage dividing resistors 14 and 15 and the first reference voltage output by the reference voltage source 13 are appropriately set.

As shown in FIG. 5, the second protection circuit 20 includes a voltage detection circuit 21, a switching element 26, and terminals 27 and 28. The voltage detection circuit 21 is also referred to as a second voltage detection circuit. The switching element 26 is also referred to as a second switching element. The second protection circuit 20 is connected to the lithium ion capacitor 40 at the terminal 27 and is connected to the second load 62 at the terminal 28. The second protection circuit 20 is connected to the grounding point 80 by the voltage detection circuit 21. The second protection circuit 20 operates by the voltage applied from the terminal 27 or 28.

In this embodiment, the switching element 26 is a p-channel MOSFET. It is assumed that the voltage detection circuit 21 is configured in the same manner as the voltage detection circuit 11 of FIG. The voltage detection circuit 21 generates a second voltage divider voltage that is divided between the terminal 27 or 28 and the ground point 80. The voltage detection circuit 21 generates a second reference voltage.

The voltage detection circuit 21 outputs a signal for controlling the switching element 26 to be turned on when the second voltage dividing voltage is equal to or higher than the second reference voltage. When the switching element 26 is an FET, the voltage detection circuit 21 outputs a signal having a voltage equal to or higher than the gate threshold voltage.

The voltage detection circuit 21 outputs a signal for controlling the switching element 26 to be turned off when the second voltage dividing voltage is less than the second reference voltage. When the switching element 26 is an FET, the voltage detection circuit 21 outputs a signal having a voltage lower than the gate threshold voltage.

The voltage detection circuit 21 is configured so that the second voltage dividing voltage becomes the second reference voltage or more when the terminal voltage of the lithium ion capacitor 40 is the second voltage or more. The second reference voltage may be the same as the first reference voltage. In this case, the resistance value of the voltage dividing resistor included in the voltage detection circuit 21 may be set so that the second voltage dividing voltage becomes the same as the first voltage dividing voltage. By making the first reference voltage and the second reference voltage the same, the reference voltage source 13 can be shared in the voltage detection circuits 11 and 21.

The time change of the terminal voltage of the lithium ion capacitor 40 will be described with reference to the graph illustrated in FIG. The horizontal axis represents the time. The vertical axis represents the terminal voltage of the lithium ion capacitor 40.

The lithium ion capacitor 40 is charged so that the terminal voltage becomes V0 until time T0, and discharge starts after time T0. At the start of discharge (time T0), the terminal voltage of the lithium-ion capacitor 40 gradually decreases due to the voltage drop due to the internal resistance of the lithium-ion capacitor 40. The terminal voltage of the lithium ion capacitor 40 drops due to discharge, and drops to the first voltage V1 at time T1.

When the terminal voltage of the lithium ion capacitor 40 becomes the first voltage V1, the first protection circuit 10 cuts off between the lithium ion capacitor 40 and the regulator 30. On the other hand, the second protection circuit 20 maintains the continuity between the lithium ion capacitor 40 and the second load 62. As a result, the power supply to the second load 62 is maintained, but the power supply to the first load 61 is stopped.

The discharge current of the lithium ion capacitor 40 is reduced by stopping the power supply to the first load 61. By reducing the discharge current, the voltage drop due to the internal resistance of the lithium ion capacitor 40 is reduced. As a result, the terminal voltage of the lithium ion capacitor 40 increases stepwise at time T1. The first load 61 stops operating at the timing when the power supply is stopped. By increasing the terminal voltage of the lithium ion capacitor 40 in a stepwise manner, the first protection circuit 10 can make the lithium ion capacitor 40 and the regulator 30 conduct again. In this case, the first load 61 may be configured so as not to automatically resume operation. For example, the first load 61 may be configured to be communicable with the external power source 8 and may be configured to resume operation when the external power source 8 acquires a signal indicating that the power supply has been restarted. By doing so, a phenomenon in which the switching element 16 of the first protection circuit 10 changes little by little between the on state and the off state (a phenomenon corresponding to chattering generated by a relay or the like) is less likely to occur.

After time T1, the lithium ion capacitor 40 discharges so as to flow the current required for the operation of the second load 62. Therefore, the discharge current after the time T1 is smaller than the discharge current before the time T1. The terminal voltage of the lithium ion capacitor 40 drops more slowly than before time T1 due to the decrease in discharge current, and drops to the second voltage V2 at time T2.

When the terminal voltage of the lithium ion capacitor 40 becomes the second voltage V2, the second protection circuit 20 cuts off between the lithium ion capacitor 40 and the second load 62. As a result, the power supply to the second load 62 is stopped.

As described above, the power control circuit 1 according to the present embodiment can function as a backup power source for supplying power to the first load 61 and the second load 62 when the external power source 8 cannot supply power. .. Further, the power control circuit 1 can preferentially supply power to the second load 62 which needs to be operated for at least a predetermined period when the charge amount of the lithium ion capacitor 40 decreases. As a result, the power control circuit 1 can back up the second load 62 for a predetermined period while functioning as a backup power source for the first load 61 and the second load 62.

The power control circuit 1 according to the present embodiment controls the opening and closing of the switching elements 16 and 26 based on the terminal voltage of the lithium ion capacitor 40. On the other hand, the power control circuit 920 according to Comparative Example 2 has a resistor 925 for detecting the discharge current of the lithium ion secondary battery 921. The resistor 925 increases power consumption, which does not contribute to load backup. The switch control unit 922 circuit itself also consumes power. The increase in power consumption in the power control circuit 920 causes a reduction in the period during which the load can be backed up. The power control circuit 1 according to the present embodiment can have a longer period during which the load can be backed up than the power control circuit 920 according to Comparative Example 2.

The lithium ion capacitor 40 can operate in a wider temperature range than the lithium ion secondary battery 921. Therefore, if the lithium ion capacitor 40 is replaced with the lithium ion secondary battery 921, the temperature range in which the power control circuit 1 can operate becomes narrow. By providing the lithium ion capacitor 40, the power control circuit 1 according to the present embodiment can expand the operating temperature range as compared with the configuration including the lithium ion secondary battery 921. As a result, high convenience can be realized.

The lithium ion secondary battery 921 tends to self-discharge due to the phenomenon that dendrite-like metallic lithium is deposited inside the lithium ion secondary battery 921. On the other hand, the lithium ion capacitor 40 is hard to self-discharge. Further, the electric double layer capacitor 915 is more likely to self-discharge than the lithium ion capacitor 40. Therefore, if the lithium ion capacitor 40 is replaced with a lithium ion secondary battery 921 or an electric double layer capacitor 915 having the same charge capacity, the period during which the power control circuit 1 functions as a backup power source is shortened. By providing the lithium ion capacitor 40, the power control circuit 1 according to the present embodiment has a longer period of functioning as a backup power source than a configuration including a lithium ion secondary battery 921 or an electric double layer capacitor 915 having the same capacity. it can. As a result, high convenience can be realized.

The lithium ion secondary battery 921 is liable to deteriorate or fail regardless of whether it is overcharged or overdischarged. On the other hand, the lithium ion capacitor 40 does not deteriorate or easily break down even if overcharge occurs. Therefore, if the lithium ion capacitor 40 is replaced with the lithium ion secondary battery 921, the power control circuit 1 needs to further include an overcharge monitoring circuit. The addition of the overcharge monitoring circuit may cause an increase in size or cost of the power control circuit 1. The power control circuit 1 according to the present embodiment does not require an overcharge monitoring circuit by including the lithium ion capacitor 40. As a result, the configuration can be simplified.

The protection of the over-discharge of the lithium ion capacitor 40 is realized by the power control circuit 1 including the first protection circuit 10 and the second protection circuit 20. That is, the power control circuit 1 can control the terminal voltage of the lithium ion capacitor 40 so that it does not become less than the second voltage, and can avoid the occurrence of over-discharge.

If the lithium ion capacitor 40 is replaced with the lithium ion secondary battery 921, the p-channel MOSFET has insufficient performance as a switching element 16 connected to the lithium ion secondary battery 921. Therefore, n-channel MOSFETs are used. By using the n-channel MOSFET, the circuit of the lithium ion secondary battery 921 needs to be switched on the ground side. When switching on the ground side, the circuit may not be grounded and may become unstable. The power control circuit 1 according to the present embodiment can operate stably as a result of switching on the high side to which a voltage is applied without switching on the ground side by providing the lithium ion capacitor 40. As a result, high convenience can be realized.

The lithium ion capacitor 40 may have a longer life than the lithium ion secondary battery 921. Therefore, the power control circuit 1 can be configured on the premise that the lithium ion capacitor 40 is not replaced. When the power control circuit 1 is configured on the premise that the lithium ion capacitor 40 is not replaced, the power control circuit 1 can be configured more simply than when it is configured to be replaceable. If the lithium ion capacitor 40 is replaced with the lithium ion secondary battery 921, the power control circuit 1 needs to be configured so that the lithium ion secondary battery 921 can be replaced. By providing the lithium ion capacitor 40 in the power control circuit 1 according to the present embodiment, the maintenance frequency can be reduced. As a result, high convenience can be realized.

If the power control circuit 1 includes a lithium ion capacitor 40 that backs up the first load 61 and a primary battery for supplying power to the second load 62 as a configuration different from that of the lithium ion capacitor 40, the power control circuit 1 is installed in the second load 62. It is necessary to provide a circuit for connecting the primary battery. Such a circuit complicates the power control circuit 1 and can be more expensive than the second protection circuit 20. Further, after the primary battery has finished discharging, the power control circuit 1 cannot function as a backup power source for the second load 62. By providing the lithium ion capacitor 40, the power control circuit 1 according to the present embodiment can be configured at a lower cost than a configuration including a primary battery, and can operate for a long period of time. As a result, high convenience can be realized.

(Automatic sleep of protection circuit)
In the first protection circuit 10, the voltage detection circuit 11 is connected to the terminal 17 connected to the lithium ion capacitor 40 via the switching element 16. That is, the voltage detection circuit 11 can receive the discharge current from the lithium ion capacitor 40 via the switching element 16. The first protection circuit 10 turns off the switching element 16 when the terminal voltage of the lithium ion capacitor 40 becomes less than the first voltage. In this case, the discharge current of the lithium ion capacitor 40 does not flow through the voltage detection circuit 11. The first protection circuit 10 does not consume power by turning off the switching element 16. In this case, the first protection circuit 10 does not consume the current of the lithium ion capacitor 40 as compared with the case where the voltage detection circuit 11 is connected to the terminal 17 without passing through the switching element 16. That is, the first protection circuit 10 does not consume unnecessary power after the first load 61 is stopped. As a result, the period during which the lithium ion capacitor 40 can supply the current to the second load 62 becomes longer.

Also in the second protection circuit 20, the voltage detection circuit 21 is connected to the terminal 27 connected to the lithium ion capacitor 40 via the switching element 26. As a result, the second protection circuit 20 does not consume the current of the lithium ion capacitor 40 after the terminal voltage of the lithium ion capacitor 40 becomes less than the second voltage. As a result, a further decrease in the terminal voltage of the lithium ion capacitor 40 can be avoided. When the terminal voltage of the lithium ion capacitor 40 is lower than the second voltage and further drops, the lithium ion capacitor 40 tends to deteriorate. Therefore, suppressing the decrease in the terminal voltage of the lithium ion capacitor 40 leads to suppressing the deterioration of the lithium ion capacitor 40.

(Charging when power is restored)
As described above, when the terminal voltage of the lithium ion capacitor 40 becomes less than the first voltage, the switching element 16 is turned off. As a result, the voltage detection circuit 11 does not operate.

Here, it is assumed that the external power supply 8 restarts the power supply when the terminal voltage of the lithium ion capacitor 40 is less than the first voltage and the switching element 16 is in the off state. It is assumed that the switching element 16 is a p-channel MOSFET.

When the external power supply 8 supplies power at a voltage equal to or higher than the first voltage, the switching element 16 is turned on. In this case, the current from the external power source 8 to the lithium ion capacitor 40 can flow through the channel of the p-channel MOSFET.

When charging the lithium ion capacitor 40 under CCCV (Constant Current, Constant Voltage) control, the external power supply 8 may supply power at a voltage lower than the first voltage according to the terminal voltage of the lithium ion capacitor 40. In this case, the switching element 16 remains in the off state. Since the switching element 16 (p-channel MOSFET) is in the off state, the current from the external power supply 8 to the lithium ion capacitor 40 cannot flow through the channel of the p-channel MOSFET.

However, the p-channel MOSFET has a parasitic diode 16a, as shown in FIG. The parasitic diode 16a is also referred to as a body diode. The switching element 16 (p-channel MOSFET) is connected so that the forward direction of the parasitic diode 16a is the direction from the terminal 18 to the terminal 17. The current from the external power source 8 to the lithium ion capacitor 40 can flow through the parasitic diode 16a. By doing so, the power control circuit 1 according to the present embodiment can restart the charging of the lithium ion capacitor 40 to the external power supply 8 without requiring a special circuit for restarting the charging. As a result, the power control circuit 1 is composed of a simple circuit.

As described above, according to the power control circuit 1 according to the present embodiment, the external power supply 8 is a lithium ion capacitor regardless of whether the switching element 16 (p-channel MOSFET) is in the on state or the off state. 40 can be charged.

It is assumed that the lithium ion capacitor 40 is replaced with the lithium ion secondary battery 921. In this case, in order to limit the overcharging of the lithium ion secondary battery 921, it is necessary to prevent current from flowing through the parasitic diode 16a. Therefore, when replaced with the lithium ion secondary battery 921, two MOSFETs connected in series so that the source-drain directions are opposite to each other are adopted as the switching element 16. Then, when the switching element 16 is in the off state, no current flows through the parasitic diode 16a, and the lithium ion capacitor 40 is not charged. Therefore, the power control circuit 1 according to the present embodiment restarts charging regardless of whether the switching element 16 is on or off when the external power supply 8 restarts the power supply for the first time by providing the lithium ion capacitor 40. it can. As a result, recovery at the time of power recovery becomes easy. Further, the resumption of charging by the power control circuit 1 can be realized by a simple circuit.

(Expansion of operating temperature range)
The upper and lower limits of the terminal voltage of the lithium ion capacitor 40 are determined according to the operating temperature of the lithium ion capacitor 40. When the lithium ion capacitor 40 is used in the temperature range from T1min to T1max, the upper and lower limits of the terminal voltage are assumed to be V1max and V1min, respectively. On the other hand, when the lithium ion capacitor 40 is used in the temperature range from T2min to T2max, the upper and lower limits of the terminal voltage are V2max and V2min, respectively. Here, it is assumed that T1max is higher than T2max. It is assumed that V1min is lower than V2min. Under such an assumption, the lower limit of the terminal voltage of the lithium ion capacitor 40 differs depending on whether the temperature of the lithium ion capacitor 40 exceeds T2max or is T2max or less. When T2max is referred to as a predetermined temperature, the lower limit of the terminal voltage is lower when the temperature of the lithium ion capacitor 40 is equal to or lower than the predetermined temperature than when the temperature of the lithium ion capacitor 40 exceeds the predetermined temperature.

As a specific example, when the lithium ion capacitor 40 is used in the temperature range from −30 ° C. to + 85 ° C., the upper and lower limits of the terminal voltage may be 3.5V and 2.5V, respectively. On the other hand, when the lithium ion capacitor 40 is used in the temperature range from −30 ° C. to + 70 ° C., the upper and lower limits of the terminal voltage may be 3.8 V and 2.2 V, respectively. In this example, each of the above variables is represented as follows.
T1min = -30 ° C, T1max = + 85 ° C
T2min = -30 ° C, T2max = + 70 ° C
V1min = 2.5V, V1max = 3.5V
V2min = 2.2V, V2max = 3.8V

As shown in FIG. 7, the lithium ion capacitor 40 may be mounted on the circuit board 100 together with the first load 61. It is assumed that the lithium ion capacitor 40 is mounted at a position affected by the heat generated by the first load 61. In this case, the temperature of the lithium ion capacitor 40 rises due to the heat generated by the operation of the first load 61. That is, the larger the calorific value of the first load 61, the higher the temperature of the lithium ion capacitor 40.

When the first load 61 is operating, the temperature of the lithium ion capacitor 40 tends to exceed a predetermined temperature. On the other hand, when the first load 61 is stopped, the temperature of the lithium ion capacitor 40 tends to stay below a predetermined temperature.

Here, it is assumed that the predetermined temperature is 70 ° C. Applying this assumption to the above-mentioned specific example, when the temperature of the lithium ion capacitor 40 exceeds 70 ° C., the lower limit of the terminal voltage is 2.5V. When the temperature of the lithium ion capacitor 40 is 70 ° C. or lower, the lower limit of the terminal voltage is 2.2V.

Further, it is assumed that the first voltage is set to 2.5V and the second voltage is set to 2.2V. Under this assumption, when the terminal voltage of the lithium ion capacitor 40 becomes less than the first voltage and the first protection circuit 10 cuts off the power supply to the first load 61, the first load 61 is stopped to cause lithium. The temperature of the ion capacitor 40 tends to stay below a predetermined temperature. Then, even if the power supply to the second load 62 continues through the second protection circuit 20 and the terminal voltage of the lithium ion capacitor 40 drops to the second voltage, it is difficult to fall below the lower limit of the terminal voltage of the lithium ion capacitor 40. ..

When the relationship between the lower limit of the temperature and terminal voltage of the lithium ion capacitor 40 and the first voltage and the second voltage in the above-described example is satisfied, the position where the lithium ion capacitor 40 is affected by the heat generated by the first load 61. It can be said that it is permissible to be implemented in. The conditions to be satisfied are paraphrased in the following (a) and (b).
(A) The lower limit of the terminal voltage of the lithium ion capacitor 40 corresponds to the first voltage when the temperature of the lithium ion capacitor 40 is higher than the predetermined temperature.
(B) The lower limit of the terminal voltage of the lithium ion capacitor 40 corresponds to the second voltage when the temperature of the lithium ion capacitor 40 is equal to or lower than the predetermined temperature.

By allowing the lithium ion capacitor 40 to be mounted at a position affected by the heat generated by the first load 61, restrictions on mounting the power control circuit 1 are reduced. In addition, the components mounted on the circuit board 100 are easily integrated. As a result, the power control circuit 1 can be downsized and reduced in cost. Further, the lithium ion capacitor 40 is utilized in the widest possible voltage range within the operating temperature range. As a result, the period during which electric power can be supplied to the second load 62 becomes longer.

(Self-stop function)
It is assumed that the first load 61 consumes the amount of power that can be supplied by the lithium ion capacitor 40 in about several tens of seconds. Here, it is assumed that the first load 61 is a processor. When the power supply from the external power supply 8 is stopped, the first load 61 detects the stoppage of the external power supply 8 and starts the stop processing of the first load 61 itself. The first load 61 can be stopped so that the operation can be safely restarted when the power supply is restarted by completing the stop processing while the power is being supplied from the lithium ion capacitor 40. The first voltage may be set so that the lithium ion capacitor 40 can continue to be discharged until the first load 61 can complete the stop processing.

After the first load 61 is stopped by itself, the regulator 30 does not have to supply power to the first load 61. The first load 61 may be connected to the regulator 30 by a communication line 73 as shown by a broken line in FIG. The first load 61 may output a discharge stop signal to the regulator 30 via the communication line 73. The regulator 30 may stop the operation of outputting the discharged electric power of the lithium ion capacitor 40 to the first load 61 and the second load 62 based on the discharge stop signal from the first load 61. By doing so, the power consumption of the regulator 30 out of the power consumption of the power control circuit 1 is reduced. Reducing the power consumption of the power control circuit 1 increases the amount of power that the lithium ion capacitor 40 can supply to the second load 62. As a result, the period during which electric power can be supplied to the second load 62 becomes longer.

Although the embodiments according to the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or modifications based on the present disclosure. It should be noted, therefore, that these modifications or modifications are within the scope of this disclosure. For example, the functions included in each component or each step can be rearranged so as not to be logically inconsistent, and a plurality of components or steps can be combined or divided into one. ..

1 Power control circuit 8 External power supply 10 1st protection circuit 11 Voltage detection circuit (12: Comparator, 13: Reference voltage source, 14: Voltage divider resistor, 15: Voltage divider resistor, 19: Nodal point)
16 Switching element 17, 18 terminal 20 Second protection circuit 21 Voltage detection circuit 26 Switching element 27, 28 terminal 30 Regulator 40 Lithium ion capacitor 51, 52 Diode 61 First load 62 Second load 71, 72 Node 73 Communication line 80 contact Point 100 Circuit board

Claims (4)

A lithium-ion capacitor that is charged by the power supplied by an external power source,
A first protection circuit that supplies the discharge current of the lithium ion capacitor when the power is no longer supplied from the external power supply to the first load that operates with the power supplied by the external power supply.
Discharge of the lithium ion capacitor when power is no longer supplied from the external power supply to a second load that operates with the power supplied by the external power supply and operates with power consumption less than that of the first load. Equipped with a second protection circuit that supplies current
The first protection circuit stops the supply of current to the first load when the terminal voltage of the lithium ion capacitor becomes less than the first voltage.
The second protection circuit is a power control circuit that stops the supply of current to the second load when the terminal voltage of the lithium ion capacitor becomes less than the second voltage lower than the first voltage. The first protection circuit includes a first switching element connected between the lithium ion capacitor and the first load, and a first voltage detection circuit for controlling the first switching element.
The first voltage detection circuit is
It is configured to be operable by the current supplied from the lithium ion capacitor via the first switching element when power is no longer supplied from the external power supply.
When the terminal voltage of the lithium ion capacitor is equal to or higher than the first voltage, the first switching element is maintained in the ON state.
When the terminal voltage of the lithium ion capacitor becomes less than the first voltage, the first switching element is transitioned to the off state.
The power control circuit according to claim 1. The first protection circuit is configured so that the lithium ion capacitor can be connected to an external power supply via the first switching element.
The power control circuit according to claim 2, wherein the first switching element is configured so that a current flows from the external power source to the lithium ion capacitor even when the first switching element is in the off state. The lithium ion capacitor is mounted on the circuit board together with the first load.
The temperature of the lithium ion capacitor increases as the calorific value of the first load increases.
The lower limit of the terminal voltage of the lithium ion capacitor is
When the temperature of the lithium ion capacitor is higher than the predetermined temperature, it corresponds to the first voltage.
The power control circuit according to any one of claims 1 to 3, which corresponds to the second voltage when the temperature of the lithium ion capacitor is equal to or lower than the predetermined temperature.

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